Inverted Amplifier Voltage Gain

Discussion in 'Homework Help' started by stubblefieldke, Mar 12, 2012.

  1. stubblefieldke

    Thread Starter New Member

    Mar 12, 2012
    Q: Determine the closed-loop voltage gain of the circuit, assuming an ideal op amp.


    My attempt:

    I set the voltage (left side of op amp) to 0 and the current into op amp to 0.
    Current at node is i1 = Vin/R.

    i1*R = i2*R because no current goes into the op amp.
    i2*R = i3*R (I am assuming this, based off of an example in my book, it may be wrong.)
    i3 + i2 = i4 = 2*i1
    i4 = i5
    i4 + i5 = i6 = 4*i1

    so the equation to find the Voltage gain is Vo = -R(i6 + i5) which, when rearranged so that Av = Vo/Vin, I get -6, however according to the book the answer is -8. What am I doing wrong? Please and thank you!